1. Technical Field
The disclosure relates to an image processing device that generates print image data to be used in print operation performed by a printing machine, and also relates to a printing machine with the image processing device.
2. Related Art
Some printing machines are equipped with a text smoothing function for making the contours of printed text look smooth. Such a printing machine performs print operation as follows.
First, the printing machine performs raster image processor (RIP) processing on data in a page description language (PDL) at a resolution higher than a print resolution. Then, the printing machine performs resolution conversion to convert the high-resolution image data (raster data) obtained by the RIP processing into low-resolution (print-resolution) image data. The printing machine performs the resolution conversion by setting the density of each pixel in the low-resolution image data to an average density of corresponding pixels in the high-resolution image data in a number determined according to the ratio between the resolutions before and after the resolution conversion. Thereafter, the printing machine performs halftone processing on the low-resolution image data to generate print image data in printable format. Then, the printing machine prints an image by use of the print image data.
When an image is printed using the text smoothing function described above, the density averaging for the resolution conversion causes an edge portion of the image, such as text, to be printed at a lower density than in a case not using the text smoothing function. This brings about an advantageous effect of making the slanted contours or the like of the text slightly blur and look smooth, but meanwhile, makes jaggedness or the like of longitudinal or lateral lines more stand out.
If, for example, a multi-drop inkjet printing machine employs the text smoothing function, an edge portion is printed at lower density. Accordingly, in pixels of the edge portion, smaller dots are formed with a smaller number of drops, than in a case not using the text smoothing function. Thereby, a slanted edge portion of a slanted text line or the like slightly blurs and looks smooth. Meanwhile, since dots are small, jaggedness or the like of a longitudinal or lateral edge portion of a longitudinal or lateral line or the like stands out because of large inter-dot gaps.
Japanese Unexamined Patent Application Publication No. 2010-45634 discloses a technique for coping with such a problem. This technique corrects the density at the edge of an image in image data whose resolution has been converted from high resolution to low resolution. Thereby, the above-described jaggedness at the edge portion of a printed image can be suppressed.